The present invention relates to the art of acoustical defect detection. The present invention finds particular application in the ultrasonic inspection of cylindrical objects such as metal pipe and tubing, and will be described with particular reference thereto. It is to be appreciated, however, that the invention has other applications including acoustical examination of sheet materials, polygonal members, rods, and the like.
Heretofore, ultrasonic transducers have been utilized in a pulse-echo mode to locate flaws and defects in an examined object. In the pulse-echo mode, an ultrasonic transducer is first caused to transmit an ultrasonic wave and then waits to receive an echo from a defect. The angle of incidence and angle of reflection relative to the surface of the defect must be equal. Thus, a transmitting transducer can only receive an echo from a defect surface which is substantially normal to the direction of ultrasonic wave transmission. Defect surfaces which are more than 5.degree. off-normal to the direction of propagation reflect the ultrasonic wave, but do not return a sufficiently large component to the transmitting transducer for the defect to be detected.
Ultrasonic transducers have been used in a pulse-echo mode to generate ultrasonic shear waves traveling peripherally around the examined object, and to detect echoes reflected peripherally back to the transducer. Axially oriented ultrasonic transducers have been used to generate axial shear waves and detect axial echoes. Similarly, ultrasonic transducers have been oriented perpendicular to the examined surface and operated in a pulse-echo mode. Further, others have oscillated or rocked the transducers to examine the object from a multiplicity of angles.
A three dimensional defect commonly has at least some surface portion which is normal to one of the pulse-echo operated transducers and is readily detected. However, a two dimensional defect, such as a crack, can only be detected by pulse-echo transducers which are oriented substantially perpendicular to the surface of the crack. Thus, peripherally oriented pulse-echo transducers and axially oriented pulse-echo transducers are only able to detect cracks which are substantially parallel or perpendicular to the axis.
It has been suggested to have ultrasonic transducers propagate ultrasonic waves around the examined object in a spiral at various angles, eg., 45.degree.. However, because the direction of propagation must be within 5.degree. of normal to a crack to be assured of detection, a wide range of wave propagation directions would be required for assuring that cracks would not go undetected.
The present invention contemplates an arrangement which overcomes the above referenced problems and others, and provides an ultrasonic inspection system which detects defects and cracks oriented at a wide variety of orientations in an examined object.